I believe that a product from USG called "Micore 300" is a suitable underlayment for tile stoveboards. It's bonded to your structure and the tile is fixed to it. Exceptional temperature insullation properties and low emissions.
Capua Custom Tile & Stone; Seattle, Washington
Member- National Tile Contractors Association
Card-carrying Schluter Systems installer
Certified WEDI Board installer
NuHeat radiant heating system "Qualified Installer"
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